Changes in blood osmolarity, electrolytes, and metabolites among adult rats treated with a neurotoxic dose of MSG 1

Abstract

Adult rats were given large doses of MSG (4 g/kg) or isosmolar amounts of sodium chloride or L-alanine intraperitoneally or by forced intubation. Blood or plasma samples from these rats where assayed for osmolarity, hematocrit, pH, and concentrations of protein, sodium, potassium, chloride, calcium, magnesium, and urea nitrogen. Intraperitoneal MSG produced characteristic hypothalamic lesions; MSG by gavage failed to do so. Intraperitoneal MSG also caused major increases in plasma osmolarity, hemoconcentration, hypovolemia, alkalosis, hypernatremia, and uremia; plasma levels of chloride and potassium fell significantly. Administration of MSG by gavage caused much smaller changes in plasma osmolarity and sodium, and no significant changes in hematocrit, plasma protein or plasma urea nitrogen. Administration of sodium chloride or L-alanine (agents not known to produce the characteristics MSG brain lesions) caused some, but not all, of the metabolic changes seen after MSG. These observations suppot the hypothesis that the ability of large, concentrated doses of MSG to produce brain lesions in susceptible species involves a two-step process, i.e., initial damage to the blood-brain barrier for glutamate, followed by entry of the circulating amino acid into the extracellular space of the brain.